How to read picture in HDC

[delio]

#include "stdafx.h"
#include "iostream"
#include "conio.h"
#include "windows.h"


using namespace std;

void main(){
	HDC hdc = GetDC(NULL);
	DWORD color = GetPixel(hdc, 500, 500);

	unsigned int r = GetRValue(color);
	unsigned int g = GetGValue(color);
	unsigned int b = GetBValue(color);

	cout << "red: " << r << endl;
	cout << "green: " << g << endl;
	cout << "blue: " << b << endl;

	system("pause");
}

From this code I think it reads pixel from screenshot
I want to read from file

I think I have to change this line
HDC hdc = GetDC(NULL);
but I don't know how to
please help me

Thank you

[knn9]

Since you use GDI(the older graphical API) I'll give a GDI answer.

#include "stdafx.h"
#include "iostream"
#include "conio.h"
#include "windows.h"


using namespace std;

void main(){
        LPCWSTR file = L"c:\image.bmp";
        HDC hdc = CreateCompatibleDC(NULL);
        HBITMAP bmp = (HBITMAP)LoadImageW(NULL, file, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
        HBITMAP hold = (HBITMAP)SelectObject(hdc, bmp);

	DWORD color = GetPixel(hdc, 500, 500);

	unsigned int r = GetRValue(color);
	unsigned int g = GetGValue(color);
	unsigned int b = GetBValue(color);

	cout << "red: " << r << endl;
	cout << "green: " << g << endl;
	cout << "blue: " << b << endl;

        SelectObject(hdc, hold);
        DeleteObject(bmp);
        DeleteDC(hdc);

	system("pause");
}

Use GetDIBBits() instead of GetPixel() if you plan to do alot of reading and writing of pixels. It'll be much faster.

[delio]

Thank you ,you save my life
Where do you learn from?

[knn9]

MSDN is a good start. Perhaps here:

http://msdn.microsoft.com/library/windows/desktop/ee663266

[delio]

Can I have another question?

I want to manually input file location from compiled program
from yours code

How can I do?

Thank you

[knn9]

You know how C++ IO works I assume? You can prompt for a filename that way. Or use command-line arguments, like so:

int main(int argc, char* argv[])
{
    //argv[1] should be first argument, argv[2] is second, etc
}

then run your program like so:

C:\>yourprog.exe image.bmp

You can open a file dialog to browse for files using the Common Item Dialog API, but that's more complicated:

http://msdn.microsoft.com/en-us/library/windows/desktop/bb776913%28v=vs.85%29.aspx

[delio]

Thanks :)